Cells growing in tissues are in a three dimensional environment with biophysical and biomechanical characteristics signals. These signals influence major cellular functions such as migration, adhesion, proliferation and gene expression.
However, most in vitro tests performed in the laboratory focus on a cell culture in two dimensions, easier to implement. In this manner, the cells are grown on plastic polystyrene dishes which are very stiff and unnatural. Adhesion of these cells on these synthetic structures is done by adhesions different from what can be found in vivo (FIG. 1). Indeed, the cell undergoes many constraints to spread and migrate in xy. The microenvironment of the cell is neglected and thus the results can give interpretations that do not correspond to what can be found in the tissues.
For about thirty years, a three-dimensional cell culture has been developing to more accurately mimic the physiology of natural tissues and organs. By this way, the cells bind to each other formants physical cell to cell bonds (FIG. 2). In addition, the material used to allow the natural three-dimensional development is malleable as natural tissues, and comprised of complex proteins in their native configuration thereby providing important biological instructions for cells. In this environment, cells can exert forces on each other by their interactions stimulating creating gap junction, by ion exchange, or even by electrical currents. These special links provide more complex phenotypes and closer to native tissues cellular functions by enhanced communication and signaling.
Two advantages are obvious for the study of pathological conditions in vitro, particularly in the search for biomarkers and new therapeutic targets and drug tests. First, the cells do not have the same response to treatment: for example, breast cancer cells grown in 2D can be easily killed by low doses of chemotherapeutic drugs and low doses of radiation. These same cells in 3D with the same doses of drug or radiation are more resistant, like cancer in vivo. Validation is therefore more accurate and representative of the actual physiology through three-dimensional tests. Second, unlike the 2D culture where cells form a very thin monolayer on the plastic surface, 3D culture show a series of cell layers. The need to diffuse through to reach the deepest cells is important. This is paramount in choosing the ideal vehicle for the desired application. Studies are also underway, including for drug delivery in this type of structure.
The development of high-throughput screening in 3D culture is proving to be an important next step in research through RNAi. Its use will allow being closer to the physiological conditions and avoiding false positives and/or false negatives inherent to the difference in environment of cells cultivated in petri dish.
To this end, products helping in the transfection of nucleic acids into eukaryotic cells in 3D scaffold are needed.